Change, as we know it directly, does not go on between fixed points such as these stages which we abstract, it goes on impartially, as it were, through the supposed stages just as much as in between them. But though fixed stages are not needed to enable change to occur, simply as a fact, they are needed if we are to describe change and explain it in terms of general laws. Qualities are assumptions required, not in order that change may take place, but in order that we may describe, explain, and so control it. Such particular qualities as red and green are really no more facts directly known than such still more general, and so more obviously fictitious notions as a colour which is of no particular shade, or a table, or a mind, apart from its qualities or states. All these fixed things are alike abstractions required for explaining facts directly known but not occurring as actual parts of those facts or stages in their change. Thus it appears that the common sense world of things and qualities and events is in the same position, with regard to the actual facts directly known as scientific hypotheses such as forces, electrons, and so on, in their various relations: none of these actually form parts of the fact, all of them are abstractions from the fact itself which are useful for explaining and so controlling it. Common sense stops short at things and qualities and events; science carries the abstraction further, that is all the difference: the aim in both cases is the same, the practical one of explaining and so controlling facts directly known. In both cases the method employed is the intellectual method of abstraction which begins by discriminating within the whole field directly known in favour of just so much as will enable us to classify it and ignoring the rest, and then proceeds to confuse even this selected amount of the actual fact with the abstract classes or other symbols in terms of which it is explained. We have just seen how the result, the worlds of common sense or science, differ from the actual facts in the way in which they change: these worlds of abstractions represent change as a series of fixed stages united by temporal relations, while the actual fact forms a continuous process of becoming which does not contain any such fixed points, as stages in relations. The more we shake ourselves free from the common sense and scientific bias towards substituting explanations for actual facts the more clearly we see that this continuous process of changing is the very essence of what we know directly, and the more we realize how unlike such a continuous process is to any series of stages in relation of succession.